This invention relates to apparatus for the measurement of the coefficient of friction between a flexible elongate material such as a yarn, thread or fiber and a cylindrical surface. More particularly, this invention concerns a portable frictometer calibrated to read directly the coefficient of friction between a yarn and the outside surface of a cylindrical roll, guide or pin.
Known frictometers such as that disclosed by Seagrave in U.S. Pat. No. 3,324,719 employ mechanisms for forwarding a yarn at a controllable, predetermined rate of speed over a stationary test surface and tensiometers for measuring the input and output tensions in the yarn traversing this surface. Friction coefficients are related to tension ratios. Strain gages for tension readings are attached to pulleys over which the yarn on the input side and output side of the pin, respectively, is made to pass. Other means for measuring input and output tension of yarn passing over a surface include the use of beam balance arms on which yarn carrying pulleys are mounted such as shown in British Pat. No. 842,919. Another frictometer type comprises, as shown in U.S. Pat. No. 2,378,614 by Zahn, a mechanism for mounting the friction surface as a roll on a pivot. A counterbalance is provided on the roll so that the angular deflection of the roll is a measurement of the difference between input and output yarn tension and, therefore, friction as yarn slides over the roll surface. Still another type of tensiometer, which might be combined into a frictometer, is disclosed by Campbell in U.S. Pat. No. 2,538,932 wherein a disc is mounted on a spring biased shaft and two pulleys are provided on the disc along a diameter thereof. Yarn passing around one pulley, through the axis of the disc and around the other pulley, in an "S"-shaped path, exerts torque against the spring bias as a result of tension in the yarn. A deflection of the disc against the spring bias is a measure of the yarn tension. Ferguson in U.S. Pat. No. 3,556,369 discloses a device for regulating tension which employs similar structure.
Although these devices operate satisfactorily for many measurement situations, none provides easy portability with direct readability of coefficient of friction after a simple easily accomplished calibration. For example, no prior instrument is known which could be taken to a yarn producing location and applied to measure the coefficient of friction of the drive roll of a yarn winding apparatus without first disassembling the windup to remove or make accessible the drive roll for measurement.